1. Field of Invention
Hops, hop extracts, beta acids, improvements in the purification of hop extracts and components thereof for their more advantageous utilization in the production of flavorings for beer, ale, and the like.
2. Background of the Invention
It is now well known that beta acids may be hydrogenolysed for conversion to 4-desoxy alpha acids, which are then converted to tetrahydroalpha acids by oxidation, which tetrahydroalpha acids have complete light stability as well as properties of improving the foam, as well as the cling and mouth feel of beer. Such beta acids were originally crystallized, or involved complicated clean up procedure, and resulted in reduced yields of the beta acids as well as the desired 4-desoxy alpha acid hydrogenolysis product. The problem is to provide beta acids of sufficient stability and purity to permit their employment in the ensuing hydrogenolysis step and to do this with elimination of catalyst poisons but without the necessity of crystallization and recrystallization, without oxidative degradation of the beta acids at some point in the process, without requiring high temperatures for the ensuing hydrogenolysis step, without significant byproduct formation, without complicated clean up procedure, and without impairment of yields either of the desired purified beta acids or the 4-desoxy alpha acid hydrogenolysis product thereof in the ensuing hydrogenolysis step.
All of the foregoing advantages are provided by the novel purification procedure of the present invention and by the thus-purified beta acids obtained thereby.
The reaction sequence for the reactions described in the foregoing is as follows: ##STR1##
3. Prior Art
The prior art is replete with methods for converting hop alpha acids into forms suitable for pre- and post-fermentation addition, as a means of improving the utilization of hops and control over the bitter flavoring imparted by hops to beer (Todd U.S. Pat. No. 3,486,906; Mitchell U.S. Pat. No. 3,949,092.). The alpha acids present in hops are normally converted during boiling of the wort to the bitter iso-alpha acids with considerable loss of yield and formation of non-bitter by-products, which disadvantages are overcome by the improvements. The hop beta acids have generally been considered a useless constituent of the hops.
It is known that normal iso-alpha acids, which are unreduced, can contribute a skunk-like aroma to beer when exposed to light, and reduction of the iso-alpha acids with borohydride reduces this effect. Improvements of this type are reported by Westermann (U.S. Pat. No. 3,798,332). Although it was recognized that beta acids could be converted to 4-desoxy alpha acids by hydrogenolysis, and the 4-desoxy alpha acids converted to tetrahydro alpha acids by oxidation, no practical method was available until Worden (U.S. Pat. No. 3,923,897 combined with U.S. Pat. No. 3,552,975). More recently, Cowles (U.S. Pat. No. 4,644,084) has disclosed an alternative for oxidizing the 4-desoxy alpha acids (made from beta acids) to transform them into tetrahydro iso-alpha acids.
Because the tetrahydro and hexahydro iso-alpha acids disclosed by Worden and Cowles have complete light stability as well as properties of improving the foam as well as the cling and mouth feel of beer, beta acids have now become of value. Improvements in the technique for converting them into hop bittering substances are consequently important. The objects of these improvements must be to improve yield, reduce cost, improve purity of product, and simplify the procedure involved.
This invention achieves these goals through a unique purification process for the beta acids which removes catalyst poisons prior to hydrogenolysis.
Worden (U.S. Pat. No. 3,552,975) describes procedure for the hydrogenolysis of beta acids. Palladium, preferably on charcoal, or platinum are the catalysts employed in this hydrogenolysis reaction involving uptake of four (4) molecules of hydrogen. In Worden's preferred experiments, recrystallized beta acid is employed as starting material. Hydrogenolysis of this material provides a product of acceptable purity in good yield. In the laboratory, recrystallization of beta acids is not a cumbersome technique, and precautions can be taken to avoid degradation of the pure beta acids, which degrade rapidly even in air. In commercial operation, however, such procedure becomes exceptionally cumbersome and prohibitively expensive. The present invention provides beta acids of equal purity without crystallization and recrystallization, and which are resistant to oxidative degradation, all aspects and improvements which are new to the art.
The procedure of Cowles, in which beta acids are precipitated from alkaline solution using carbon dioxide, is acceptable if high temperatures are to be used for the subsequent hydrogenolysis. However, under the conditions of Cowles, by-product formation is significant, clean-up procedure is complicated, and yields of desired 4-desoxy alpha acid are impaired. The present invention obviates these problems by allowing low-temperature, low-pressure hydrogenolysis of the purified and stable beta acid product of the invention.